First person present or past?

Just started a thread on authonomy.com about writing in first person present or first person past and it brought up / is bringing up a lot of interesting stuff. The majority of books you read are written in the past tense, my 1st 3 were, it suited the 3rd person multiple POV style. But there are a hell of lot of them written in FPP (first person present) and readers don't even realise. Those books which used / use it are GREAT books, I'll just ring off a few...The Hunger Games, The Help, Trainspotting, and even Fifty Shades of Gray(I think perhaps I meant GREAT in terms of sales). I even found FPP in 'Disgrace' by Coetzee. If that ain't a stamp of approval, I don't know what is.
So, I'm experimenting. It's interesting. Some actions by my new Main Character (MC) seemed right in present, so I made the MC's action present, while all other actions past. It's strange but it seems to work.
...mmm, maybe I know why...YOU do something now, it happens in the present, whereas what YOU see has already been 'decided' before you see it, so it's in the past, even if it's a continuing process. Get it? I think I'll continue on, perhaps I'll crack it or not.